Method for measuring and compensating gain and phase imbalances in quadrature modulators

Inactive Publication Date: 2004-08-26
ENVARA
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Problems solved by technology

Quadrature modulators (sometimes referred to as IQ modulators), in particular those used in RFIC (Radio Frequency Integrated Circuits) operating at high frequencies in the GHz range, may incur significant gain and phase imbalances in the base-band path, as well as orthogonality phase imbalance in the local oscillator path.
The effect of these impairments, generally denoted as gain and phase imbalances (or "IQ" imbalance), is distortion of the transmitted signal, which translates to re

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  • Method for measuring and compensating gain and phase imbalances in quadrature modulators
  • Method for measuring and compensating gain and phase imbalances in quadrature modulators
  • Method for measuring and compensating gain and phase imbalances in quadrature modulators

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Embodiment Construction

[0033] I(t), Q(t) sine / cosine waveforms with equal amplitude and frequency, but shifted by 90 degrees one with respect to the other, e.g.:

I(t)=A cos (.omega..sub.it-90.degree.)=A sin (.omega..sub.it)

Q(t)=A cos (.omega..sub.it)

[0034] Ignoring the modulator imbalance we get:

Y(t)=A sin (.omega..sub.it) sin (.omega..sub.LOt)+A cos (.omega..sub.it) cos (.omega..sub.LOt)=A cos [(.omega..sub.LO-.omega..sub.i)t] (5)

[0035] i.e. the output contains a single sideband carrier at frequency f.sub.LO-f.sub.i=(.omega..sub.LO-.omega..sub.i) / 2.pi.. Now, for the same sine inputs waveforms, we compute the effect of gain and phase imbalances:

Y(t)=A(1+.epsilon.) sin (.omega..sub.it+.DELTA..epsilon.) sin (.omega..sub.LOt+.DELTA..phi.)+A cos (.omega..sub.it) cos (.omega..sub.LOt) (6)

[0036] By standard trigonometric manipulation we can show that:

Y(t)=S.sub.L cos [(.omega..sub.LO-.omega..sub.i)t+.psi..sub.L)+S.sub.U cos [(.omega..sub.LO+.omega..sub.i)t+.psi..sub.U) (7)

[0037] where: 1 S L = A ( 1 + ) cos 2( -...

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Abstract

A simple and efficient method to measure base-band gain and phase imbalance as well as orthogonality phase imbalance in a quadrature (IQ) modulator (12). The method comprises estimating values of modulator gain and phase imbalances (34) while the modulator is operational, by inputting at least one test signal at a base-band frequency 2 fi and computing the imbalances based on the 2 fi term, the computed imbalances then used in normal transmit operation to generate a pre-distortion transformation on the transmit signal to generate an imbalance compensation. The method can be easily expanded to cope with frequency dependent base-band amplitude and phase imbalance. This feature has an advantage when the transmitted signal is a multi-carrier signal, as the compensation can be adapted for each individual carrier.

Description

FIELD AND BACKGROUND OF THE INVENTION[0001] The present invention relates to measurement and calibration of quadrature modulators as used in transmitters for digital communication. Quadrature modulators (sometimes referred to as IQ modulators), in particular those used in RFIC (Radio Frequency Integrated Circuits) operating at high frequencies in the GHz range, may incur significant gain and phase imbalances in the base-band path, as well as orthogonality phase imbalance in the local oscillator path. The effect of these impairments, generally denoted as gain and phase imbalances (or "IQ" imbalance), is distortion of the transmitted signal, which translates to reduced or even unacceptable performance.[0002] In many cases it is not practical, and sometimes even not feasible, to design and build quadrature modulators with sufficiently low values of gain and phase imbalances. However, if the quadrature modulator gain and phase imbalances can be estimated, there exist known methods to co...

Claims

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Application Information

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IPC IPC(8): H04L1/24H04L27/00H04L27/26H04L27/36
CPCH04L1/244H04L2027/0016H04L27/364H04L27/2626
Inventor NADIRI, ZIVI
Owner ENVARA
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